from that direction). Antenna sizes are typically those of domestic TV aerials, and
consequently most inconspicuous (compare that with your "Silver Rod" lightning
Another development on the Amateur Radio scene is the data-handling
repeater. This is a land based device which receives data signals on one channel
and re-transmits them on another, with a considerable improvement in range (up to
20 miles). One such repeater is GB3MT (Bolton) which will handle ASCII & CCITT No.2
codes and even permit interconversion, i.e. an incoming ASCII (cUTS) transmission
being recoded and transmitted in CCITT code and vice-versa. Another facility
offered is that of "electronic letterbox". This allows the reception, storage and
later retransmission of messages and data. More of these devices are being planned!
Television transmissions are permitted by the Amateur licence on a number
of bands from 432 MHz upwards, and I have made use of the video output from the
Nascom 2 to transmit messages and graphics displays on this band over distances of
up to 6 miles with 4 watts PEP. A light-pen project is planned shortly to allow
onscreen message writing!
Digital Tape Storage
With so much information on floppy disk systems having appeared in the
first edition of 80-BUS News (and jolly interesting it was too!), I feel I must
take up the challenge thrown down in the editorial, and write something about my
(non-disk) system which uses digital tape storage. I decided to go for this form of
mass storage about a year ago, when disk storage seemed too expensive (it still
does) and under-developed for the Nascom, and a device called CFS appeared on the
market, produced by Grange Electronics. This unit is based upon the Philips DCR
which takes mini-cassettes of the kind used in pocket dictaphones.
I don’t intend to inflate this into a full review of the CFS as I am not
even sure that it is still being sold, so, briefly, it provides 96k storage (48k
per side) in 24 x 2k blocks + directory block (1 each side) on each mini-cassette
tape. The unit plugs into the PIO port on the Nascom 2, and is driven by a 2k
operating system called CASSOP (the source listing of which is readily available).
This 0.S. allows tape formatting, file writing, reading, renaming and deletion, and
contains subroutines which are accessible from external software. I have so far
successfully interfaced several system programs with it, including NAS-PEN, Xtal
Basic, Nascom Basic, ZEAP2 and a data-file handling program, via Nas-Sys.
All my software now resides either on mini-cassette, or in EPROM held on
the Gemini EPROM card and "paged" in and out of the memory map by a boot-loader
based upon David Parkinson’s excellent scheme outlined in INMC80-4. This loader
copies Nas-Sys into RAM and then optionally overlays the R,W and V routine
addresses in the jump table with addresses of routines in the loader which
communicate with the tape operating system. If the overlay is not invoked, normal
audio tape I/O (or data transmissions) may take place.
One shortcoming of the CASSOP system is that no “interlock” is provided to
query a "Prepare Tape" command, which is accidentally invoked. Thus the directory
can be scrubbed in no time flat (certainly before you realize what is going on and
hit the reset button!). Since this has happened to me (twice), I have written a 2k
tape salvage program which runs under Nas-Sys 3 (or 1 with simple changes) and
allows access to the individual blocks on tape, with screen editing of directory,
data blocks and read/write/verify etc. I wonder how many other CFS users have had
similar problems and could use this program.
All in all, I think the tape system works very well, giving named file
facilities and operation under software control, even though it can’t match the
random access speed of disks; AND it cost about £170 – a lot cheaper than any disk
systems around at the moment (although I wonder if the Sinclair Microdrives could
be "bent" to work on a Nascom ??).